Staircases have existed almost since the beginning of time. Many types of materials have been used in making stairs. In most residential construction, stairs are built from lumber. A typical staircase has two main parts: the risers and the treads. The risers are boards that are cut in a notch pattern, at some angle, to form the base of the stairs. Usually two or three risers are needed to form a staircase. The treads are boards cut to fit across the risers. The treads are attached to the risers by placing them into the notches on the risers. When the risers are set at the proper angle, the treads lie flat in an ascending or descending pattern. The process of cutting the riser boards is one of the skills that every carpenter must learn. This process involves calculating the number of treads needed for a given space, the size of the treads, and the length of span to be covered. A framing square is often used to lay out the placement of the notches on the riser boards. Once the series of notches has been marked, the boards can be cut.
Despite the availability of tools that make this layout and cutting easier, it is still a time consuming and error prone operation. One mistake in layout or cutting results in wasted wood and time. Several attempts at reducing the potential for error have been developed. These typically take the form of pre-measured and pre-formed stair assemblies.
Examples of the pre-measured stair assemblies can be found in U.S. Pat. Nos. 960,412, 1,701,659, 1,166,428, 2,377,994 and 5,357,724. These designs use a pre-made stair tread and some type of pre-formed supporting structure. These systems completely remove any guess work or field cutting to form the stairs. Most of these systems use metal to form the stair structures.
A second type of system has also been developed. In this system, parts are field assembled to make a stair. Examples of these stairs are found in the following patents. U.S. Pat. No. 3,978,628 shows a pre-formed tread and riser in one piece. Each piece has a set of tabs and slots that interlock with other pieces. In this way, several of these units can be connected to form a stair. U.S. Pat. No. 4,422,270 teaches use of angle brackets. These brackets are arrayed in pairs that are bolted together. A separate tread is then bolted to the top of the brackets. This assembly can then be bolted to the building framing to make a completed stair. U.S. Pat. No. 4,593,503 uses a pair of scissors linkages to form the risers for the stair. These linkages can be set at any desired angle and are then bolted to the framing for support. The linkages have flanges that hold the treads, which can be made of wood or other materials. Finally, U.S. Pat. No. 4,951,434 teaches use of a set of angled riser supports and a set of pre-formed stairs. Each stair has a tread and the body of a riser formed into one piece. Each stair bolts to the riser supports to form the staircase.
Although all of these designs have some benefits, they also have inherent problems. In most cases, the pre-formed stairs are sized at the factory. There is no easy way to adjust them in the field. This means the staircase must be designed to accommodate the fixed sizes of the components. In other cases, special framing is required to support the assemblies. This reduces the benefits of such stairs as material and labor are need for the framing. Also, many of the bolt-together stairs shown require a substantial number of bolts, which slows down the assembly time.